Support custom headers. (#289)

Author: YoEight

db-client-java/src/main/java/com/eventstore/dbclient/ConnectionMetadata.java

@@ -2,6 +2,8 @@
 
 import io.grpc.Metadata;
 
+import java.util.Map;
+
 class ConnectionMetadata {
     private Metadata metadata;
 
@@ -27,6 +29,13 @@ public ConnectionMetadata requiresLeader() {
         return this;
     }
 
+    public ConnectionMetadata headers(Map<String, String> headers) {
+        for (Map.Entry<String, String> entry : headers.entrySet())
+            this.metadata.put(Metadata.Key.of(entry.getKey(), Metadata.ASCII_STRING_MARSHALLER), entry.getValue());
+
+        return this;
+    }
+
     public Metadata build() {
         return this.metadata;
     }

db-client-java/src/main/java/com/eventstore/dbclient/GrpcUtils.java

@@ -150,6 +150,8 @@ static public <S extends AbstractAsyncStub<S>, O> S configureStub(S stub, EventS
             metadata.requiresLeader();
         }
 
+        metadata.headers(options.getHeaders());
+
         return finalStub.withInterceptors(MetadataUtils.newAttachHeadersInterceptor(metadata.build()));
     }
 }

db-client-java/src/main/java/com/eventstore/dbclient/OptionsBase.java

@@ -1,10 +1,14 @@
 package com.eventstore.dbclient;
 
+import java.util.HashMap;
+import java.util.Map;
+
 class OptionsBase<T> {
     private Long deadline;
     private final OperationKind kind;
     private UserCredentials credentials;
     private boolean requiresLeader;
+    private Map<String, String> headers = new HashMap<>();
 
     protected OptionsBase() {
         this(OperationKind.Regular);
@@ -83,6 +87,15 @@ public T deadline(long durationInMs) {
         return (T)this;
     }
 
+    /**
+     * Adds a custom HTTP header that will be added to the request.
+     */
+    @SuppressWarnings("unchecked")
+    public T header(String key, String value) {
+        headers.put(key, value);
+        return (T)this;
+    }
+
     Long getDeadline() {
         return deadline;
     }
@@ -98,4 +111,8 @@ boolean isLeaderRequired() {
     UserCredentials getCredentials() {
         return this.credentials;
     }
+
+    Map<String, String> getHeaders() {
+        return this.headers;
+    }
 }